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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 701 |
| 7 | 4774 |
| 8 | 37128 |
| 9 | 324576 |
| 10 | 3153961 |
| 11 | 33709743 |
| 12 | 393044544 |
| 13 | 4964774568 |
| 14 | 67536381485 |
| 15 | 984328864872 |
| 16 | 15302821821071 |
| 17 | 252773481889854 |
| 18 | 4420945845050347 |
| 19 | 81616873102658977 |
| 20 | 1586065426493434829 |
| 21 | 32363206963164145993 |
| 22 | 691807691094619216393 |
[1,1,2,6,24,120,701,4774,37128,324576,3153961, 33709743,393044544,4964774568,67536381485, 984328864872,15302821821071,252773481889854, 4420945845050347,81616873102658977, 1586065426493434829,32363206963164145993, 691807691094619216393] |